docs: def script_to_hex(script):
      """ Parse the string representation of a script and return the hex version.
          Example: "OP_DUP OP_HASH160 c629...a6db OP_EQUALVERIFY OP_CHECKSIG"
      """
      hex_script = ''
      parts = script.split(' ')
      for part in parts:
          if part[0:3] == 'OP_':
              try:
                  hex_script += '%0.2x' % eval(part)
              except:
                  raise Exception('Invalid opcode: %s' % part)
          elif isinstance(part, (int)):
              hex_script += '%0.2x' % part
          elif is_hex(part):
              hex_script += '%0.2x' % count_bytes(part) + part
          else:
              raise Exception('Invalid script - only opcodes and hex characters allowed.')
      return hex_script